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Objective: Whereas increased urinary excretion of type IV collagen, which is believed to reflect renal overproduction of this extracellular matrix protein in early diabetic nephropathy, has been confirmed in several studies, examination of serum concentrations of this analyte has yielded conflicting results. We sought to clarify the relationship between early renal dysfunction in diabetes and circulating type IV collagen concentrations., Research Design and Methods: We measured serum (human) collagen IV concentrations by immunoassay in 109 patients with type 1 or type 2 diabetes and various amounts of albuminuria extending from the normo- to the macroalbuminuric range, and we examined its relationship to albumin excretion and to serum creatinine levels., Results: Serum collagen IV concentrations (mean +/- SEM) were not significantly different in normoalbuminuric (219 +/- 10 ng/ml), microalbuminuric (209 +/- 6 ng/ml), or macroalbuminuric (206 +/- 7 ng/ml) diabetic subjects or in nondiabetic normal volunteers (206 +/- 10 ng/ml). Collagen IV concentrations showed no significant correlation (P > 0.25) with albumin excretion (r = -0.001), HbA(1c) (r = 0.030), or serum creatinine (r = -0.161) and were unrelated to urinary excretion of collagen IV in the subset of subjects in whom these data were available., Conclusions: The results of this cross-sectional analysis discount the utility of measurement of the serum concentration of collagen IV as an indicator of early renal dysfunction in diabetes. Increased urine excretion of collagen IV without a significant change in the serum concentration is consistent with a renal origin of this analyte in early diabetic nephropathy.

Objective: Increased albumin excretion in diabetes is believed to be derived from hemodynamic and/or permeability abnormalities, whereas mesangial matrix expansion gives rise to the reduction in glomerular filtration surface and decline in renal function in diabetic nephropathy. We postulated that the overproduction of extracellular matrix proteins underlying glomerulosclerosis in diabetes might be associated with the excretion of increased amounts of type IV collagen in the urine., Research Design and Methods: To explore this hypothesis, we measured the urinary excretion of (human) collagen IV by immunoassay in 65 patients with type 1 or type 2 diabetes and various degrees of albuminuria and examined its relationship to filtration function assessed by the reciprocal of the serum creatinine (RSC)., Results: Collagen IV excretion showed a significant (P < 0.001) inverse correlation (r = -0.62) with the RSC, and this correlation pertained regardless of whether albumin cxcretion was in the low (< or =< or = 100 microg/mg creatinine r = -0.73) or high (>100 microg/mg; r = -0.53) range. In contrast, albumin excretion showed insignificant correlation with either collagen IV excretion (r = 0.12) or with the RSC (r = -0.20). Urinary collagen IV was significantly higher (P < 0.05) in patients with an RSC value < or = 100 (28.3 +/- 2.4 ng/mg creatinine) than in patients with an RSC value > 100 (16.0 +/- 0.8 ng/mg creatinine)., Conclusions: Because not all patients with microalbuminuria progress to declining renal function and some patients who develop nephropathy do not manifest albuminuria, the findings in this cross-sectional analysis suggest that measurement of urine collagen IV may be a useful noninvasive indicator to detect diabetic renal disease entering a phase of compromised renal function.

Albumin modified by Amadori-glucose adducts induces coordinate increases in the expression of extracellular matrix proteins, transforming growth factor (TGF)-beta1, and the TGF-beta type II receptor in glomerular mesangial cells. Because activation of protein kinase C (PKC) accompanies the increased mesangial cell expression of matrix proteins and TGF-beta1 induced by high ambient glucose, we postulated that glycated albumin (GA) modulates PKC activity and that PKC participates in mediating the GA-induced stimulation of matrix production. To test this hypothesis, we examined the effects of PKC inhibitors on collagen type IV production by mouse or rat mesangial cells incubated with GA, and the influence of GA on PKC activity in these cells. Increased collagen type IV production evoked by GA in 5.5 and 25 mM glucose in mouse mesangial cells was prevented by both general (GF-109203X) and beta-specific (LY-379196) PKC inhibitors. Total PKC activity, measured by phosphorylation of a PKC-specific substrate, increased with time after exposure of rat mesangial cells to GA compared with the nonglycated, glucose-free counterpart. GA caused an increase in PKC-beta1 membrane-bound fraction and in total PKC activity in media containing physiological (5.5 mM) glucose concentrations in rat mesangial cells, confirming that the glucose-modified protein, and not a "hyperglycemic" milieu, was responsible. The findings indicate that Amadori-modified albumin stimulates mesangial cell PKC activity, and that activation of the PKC-beta isoform is linked to the stimulation of collagen type IV production.